Serena comes through battle with Stosur

Serena Williams rallied in both tiebreakers to secure a straight sets win over Samantha Stosur on Wednesday in her opening match at the Cincinnati Masters.

The world No.1 battled through to prevail 7-6(7) 7-6(7) against the former US Open champion in one hour and 54 minutes, with each player squandering their solitary chance to break.

"She was serving so well so I told myself, 'I can't be broken because if I'm broken she'll probably end up winning the set,'" said Williams, who next faces either Flavia Pennetta or Taylor Townsend in the third round

"I played well, considering how amazing Sam played. I'm trying not to be so hard on myself."

Elsewhere, third seed Petra Kvitova struggled with her serve as she went down 6-2 7-6(2) to Elina Svitolina.

The Wimbledon champion made nine double-faults and landed just 52 percent of her first serves through the match.

"I'm disappointed how I played today, for sure," Kvitova said. "From the beginning, I didn't feel very comfortable out there."